1. Field of the Invention
The present invention relates to an inspection apparatus, an inspection method, and a manufacturing method of a pattern substrate, and more particularly, to an inspection apparatus, an inspection method, and a manufacturing method of a pattern substrate using an optical scanning.
2. Description of Related Art
A defect inspection apparatus detecting surface defect of a semiconductor wafer, a mask blank, or a photo mask or the like has recently been used in order to improve manufacturing yield of a semiconductor device. In the defect inspection apparatus, there has been a strong demand for performing the inspection with high accuracy in high spatial resolution along with the increasing miniaturization of LSIs.
As the defect inspection apparatus detecting such a micro defect, the defect inspection apparatus employing a confocal optical system has been known (Japanese Unexamined Patent Application Publication No. 2003-4654). FIG. 8 is a diagram showing a conventional inspection apparatus employing a confocal optical system. As shown in FIG. 8, a light beam emitted from a laser source 1 is made incident on an objective lens 3 through a half mirror 2 which functions as a beam splitter. The objective lens 3 focuses the incident light beam into a micro spot beam and projects the micro spot beam on a sample 7 provided on a stage 8. The reflected beam from the surface of the sample 7 is reflected by the half mirror 2 to be made incident on a light receiving element 6a of a photodetector 6 through a relay lens 5 and a spatial filter 9 having a pin hole 9a. 
In the confocal optical system, the beam reflected from the sample surface provided in a focal position of the objective lens 3 can transmit the pin hole 9a whereas the reflected beam from the sample surface which is deviated from the focal position cannot transmit the pin hole 9a, which decreases the output signal intensity of the photodetector 6. Therefore, the defect of the sample surface can be detected from the output signal intensity from the photodetector 6. Further, a light blocking plate 4 is provided on an optical path of the light beam reflected by the half mirror 2. The light blocking plate 4 blocks half of the light on one side in a direction corresponding to a scan direction of the light spot on the surface of the sample 7. Hence, it is possible to change beam amount that is made incident on the light receiving element 6a depending on a defect shape to detect the defect shape.
However, these defect inspection apparatus cause problems as follows. The half of the detection light is blocked in the conventional defect inspection apparatus, which causes loss of intensity of the output signal generated by receiving the detection light. Therefore, the output signal is susceptible to shot noise or thermal noise. In the typical defect inspection of a semiconductor wafer, the generated output signal is compared with positive/negative limit value (slice level). When the comparison result exceeds the slice level, it is determined that there is a defect. Therefore, false detect is often generated in the conventional technique. False detection is occurred when there is no real defect but the output signal exceeds the slice level due to noise. When the slice level is made lower in order to improve the detection sensitivity against the real defect, probability of occurring the false detect is increased, which means it is difficult to improve the detection sensitivity against the real defect. Further, when the intensity of the beam which is made incident on the defect is fluctuated by the noise or the like to generate top/bottom asymmetric signal, the detection accuracy degrades.
To overcome the above-described problem, we suggested the inspection apparatus in which the light spot focused on the sample scans the region where the light spot overlaps the light spot of the adjacent scan line so as to illuminate the region (Japanese Unexamined Patent Application Publication No. 2006-125967). In such an inspection apparatus, it is determined whether there is a defect candidate detected by light spots a and b that are adjacent to each other within a certain distance as shown in FIG. 10. Then the false defect is eliminated and only the real defect is detected.
However, in the conventional inspection apparatus, it is impossible to perform high-speed inspection since the light spot focused on the sample scans the region where the light spot overlaps the light spot of the adjacent scan line so as to illuminate the region.
Further, the beam profile of the light beam that is emitted from the laser source typically shows a normal distribution characteristic having a peak at the center. Therefore, the detection sensitivity of the defect degrades as the position of the defect is away from the center of the light spot focused on the sample. As shown in FIG. 11, even when the defect is positioned at the center of a light spot a, this defect is positioned at the edge of an adjacent light spot b, which means the detection sensitivity by the light spot b degrades. The problem as stated is also caused even in the surface inspection other than the semiconductor wafer such as defect detection of mask blank for manufacturing a semiconductor device.
The present invention has been made in view of the above circumstances. One object of the present invention is to provide an inspection apparatus, an inspection method, and a manufacturing method of a pattern substrate that are able to perform inspection with fewer loss of the signal intensity, with high detection sensitivity, and with high speed.